The present invention relates to truck-mounted brakes for a railroad vehicle and more particularly to an improved single actuator for truck mounted brakes.
The accepted truck mounted brakes throughout the railroad industry approved by AAR is a double actuator system known as NYCOPAC sold by New York Air Brake Corporation and its equivalent WABCOPAC sold by Westinghouse Air Brake Corporation. Two actuators are used, one connected to each brake beam on opposite sides of the center axis. An example of the structure is illustrated in U.S. Pat. No. 3,499,507. The next generation of truck mounted brake includes a single actuator, truck mounted brake assembly known as NYCOPAC II and WABCOPAC II. This structure includes a single actuator with a pair of force transmitting arms and a lever connected to the opposite, brake beam. A typical example of this structure is illustrated in U.S. Pat. No. 4,793,446.
As illustrated in U.S. Pat. No. 3,499,507, the slack adjuster is provided on the opposite end of the force transmitting device from the actuator and in the opposing brake beam. The NYCOPAC and WABCOPAC have no slack adjuster. In the single actuator system illustrated in U.S. Pat. No. 4,793,446 the slack adjuster is on the return force transmitting device. It is important that the force transmitting elements and the slack adjuster do not intersect the openings in the bolster for the various angular positions of the force transmitting elements.
The single actuator, truck mounted brake provides a force generated by the brake cylinder multiplied by a factor of four. This system is very effective as a force generated by the brake cylinder is transferred to the center of the arc of each of the shoes equally. The center of the force in the middle of each of the shoes eliminates wasted torsional components that exist in other systems.
The NYCOPAC II including a double acting slack adjuster brake cylinder having air on one side of the piston to apply the brakes and a spring return. The hand brake is connected to the piston directly by a series of cables, rods and chains. Since the hand brake worked directly on the piston, the slack adjuster operated the same when actuated by air as well as the hand operated brakes. In a single actuator system illustrated in U.S. Pat. No. 4,793,446, wherein the slack adjuster is in the return force transmitting element or device, the hand brake has been applied at the output of the actuator prior to the slack adjuster. This structure, as illustrated in U.S. Pat. Nos. 4,771,686 and 5,069,312, applies a single force in a common direction to the slack adjuster and thus is similar to operation to the NYCOPAC II without the use of cables or connection to the piston itself, internal the brake cylinder.
When one attempts to incorporate a hand brake connected to the output of the actuator where the actuator includes the slack adjuster thereby eliminating the cables from the NYCOPAC II, dangerous situations may be produced. The pulling forces produced by the hand brake are substantially larger than the pushing force produced by the pneumatic actuated piston. This could detrimentally affect and possibly destroy the slack adjuster. Also, if the actuator is not operated by air after replacement of brakes; the elements within the slack adjustor are not in their appropriate position and an application of the hand brake would not produce a slack adjusting operation. Thus, either the hand brake will not apply the brakes in one situation or the hand brake will produce a force which could destroy or severely damage the slack adjuster in the other extreme.
Thus, it is an object of the present invention to provide an improved single actuator and slack adjuster for use with hand brakes.
Another object of the present invention is to provide a single actuator and slack adjustor for truck mounted brake systems which will operate the same for pneumatic as well as hand brake actuation.
These and other objects are attained by a slack adjuster for use in combination with a pneumatic brake actuator cylinder wherein the slack adjuster includes a friction clutch which prevents rotation of the screw for a first relative position of the screw and piston, while allowing rotation of the screw :for excess force on the ram pulling the screw to relative position beyond the first relative position. A second clutch, which is a standard toothed clutch, prevents rotation of the screw for second relative position of the piston and screw when pressure is applied. The screw rotates when clutches are disengaged. A spring biases the piston in opposition to the fluid pressure which actuates the cylinder. In response to fluid actuation, the piston and screw are in the first relative position with the friction clutch engaged at the beginning of the extension of the ram and in second relative position, with the toothed clutch engaged, at the end of the ram extension. In response to the pulling force on the ram, the piston and screw are in the first relative position with the friction clutch engaged at the beginning and the end of the extension of the ram with correct cylinder slack. The hand brake is connected to the ram extending from the combined actuator slack adjuster. The hand brake may operate on the ram directly or through the brake beams.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.